The present invention refers to a pull clamp for attaching to sheet metal flanges, folds and the like for transmission of pulling forces to a piece of sheet metal, particularly in collision repair or alignment operations on damaged vehicle bodies etc. The clamp comprises two opposed clamping jaws which are tightened against each other by bolts. One end of the clamp includes opposite clamping surfaces for engagement with the sheet metal flange or fold, wherein the jaws enclose a connecting member for coupling to a pulling means, with the member including a conical wedge element for exerting a spreading-apart action on the inner surfaces of the jaws to increase the clamping force between the clamping surfaces of the jaws in proportion to the pull of the pulling means.
Pull clamps are previously known for transmitting pulling forces from a pulling means such as an hydraulic power cylinder to the edge of one or more sheet metal pieces or to a sheet metal fold. It has turned out to be difficult, however, to obtain a reliable attachment to the sheet metal edge through only the clamping force from bolts positioned between the jaws, particularly for greater pulling forces. Various design suggestions therefore have been made for allowing a greater or smaller increase of the clamping force at the clamping surfaces of the jaws by means of the applied pulling force.
Initially said designs operated satisfactorily only when the pulling force acted in the plane of the sheet metal edge or fold and at right angles to the longitudinal direction thereof. When in other oblique directions to the longitudinal direction, the pulling force still had a tendency to pull off the clamps from their engagement with the sheet metal. An attempt to eliminate this drawback of known pull clamps has been made in a structure disclosed in the Swedish patent specification No. 222,495. While the pull clamp described therein has been able to stand pulling forces within a smaller angle to a perpendicular to the sheet metal edge or fold, as attempt at greater angles to the perpendicular the connecting member has resulted in an opposite action along the portion of the clamping surfaces closest thereto, namely a reduction of the clamping force between said surfaces. There is, however, an ever increasing demand for a pull clamp, particularly in today's collision repair equipments, which allows the application of pulling forces within a range from at right angle to the longitudinal direction of the fold to parallel thereto without impairing the clamping force between the clamping surfaces at any portion thereof.